Air/oil lubricators or machines are new development in lubrication industry. It utilizes the high speed compressed air to carry the lubricant (oil) such that the lubricant will only travel along the tube or pipe walls in a form of a thin film. By properly controlling the air flow, the lubricant can be precisely delivered to the points where lubrication is required. This is to compare the prior oil mist lubricating technology that the compressed air impacts onto the lubricant making it into a misty formality and then the lubricant mist hits the lubricating points. Such a process is therefore neither environmentally friendly nor cost effective for lubricant. The new air/oil lubricating process separates the air and lubricant resulting in the air released after lubricating points will preserve its air composition whilst the lubricant can be precisely dosed. Hence the new process is environmental friendly and can save significant amount of lubricants. However, the new technology will require the precise control of the flow of the lubricant so that the discontinuity of the lubrication would not take place. The prior technology of proximity switch can monitor the lubricant flow but it cannot measure the air flow and has a slow response with tens of seconds. This invention hence make it possible for a more precisely control of the lubrication process, substantially enhance the reliability, and an overall cost reduction. The sensors can also be applicable to other two phase (gas and liquid) flow measurement, monitor and control.